JP2012125662A - Concentrated-seawater discharge method for seawater desalination apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that if concentrated seawater, discharged from a seawater desalination apparatus, is discharged in a sea area, salinity of the sea area becomes higher than salinity of an ordinary sea area due to high salinity of the concentrated seawater, so that fear for influence to a marine ecosystem is generated, therefore a dilution method for diluting the concentrated seawater with seawater is adopted as a countermeasure, but it is hard to reduce the salinity to the ordinary seawater.SOLUTION: In the seawater desalination apparatus 3, the seawater taken is pressurized to be permeated through a reverse osmosis membrane, so that permeated water is obtained and the concentrated seawater impermeable through the reverse osmosis membrane is discharged to the outside of an system. The concentrated seawater from the seawater desalination apparatus 3 is mixed with treated water discharged from a sewage treatment plant and the mixed concentrated seawater, mixed with the treated water, is discharged to the sea area.

Description

  The present invention relates to a concentrated seawater discharge method discharged from a seawater desalination apparatus, and more particularly, to a concentrated seawater discharge method of a seawater desalination apparatus suitable for reducing the influence on the ecosystem of the discharge area of the concentrated seawater.

  A reverse osmosis membrane water generator equipped with a reverse osmosis membrane module is used for a seawater desalination device using seawater as raw water. Generally, after turbidity in seawater to be collected is agglomerated, a sand filter or an MF membrane is used. A means for removing turbid components after the coagulation treatment by membrane filtration using the like, and supplying pressurized water to the reverse osmosis membrane device as supply water to obtain permeated water is adopted. In addition, microorganisms, algae, etc. exist in seawater, but if they adhere to the reverse osmosis membrane surface and proliferate, they will cause biofouling. In order to sterilize, a chlorine injection process in which a chlorine-based disinfectant such as chlorinated water or sodium hypochlorite having persistence is injected is employed.

  In such a seawater desalination apparatus, the permeated water that has passed through the reverse osmosis membrane is obtained as fresh water, while the concentrated seawater in which the salt that has not passed through the reverse osmosis membrane is concentrated is discharged. The salinity of the concentrated seawater discharged from this seawater desalination apparatus increases as the permeate recovery rate increases. When the permeate recovery rate is 40% to 60%, the salinity of concentrated seawater is about 6% to 8%, about 1.7 to 2.5 times that of normal seawater (dissolved NaCl, about 3.5%). However, it is currently discharged directly into the water intake area.

  In this case, there is concern about the impact on the marine ecosystem due to the release of high-concentration concentrated seawater to the sea area. For this reason, for example, as known in [Patent Document 1], when concentrated seawater is discharged, there is a method in which it is mixed with seawater having a lower salinity concentration than concentrated seawater and discharged with a lower salinity concentration of concentrated seawater. Proposed. However, in order to dilute the concentrated seawater with seawater, as shown in Fig. 13, the amount of seawater more than a dozen times the amount of concentrated seawater to be discharged is mixed as shown in the relationship between the seawater mixing ratio and the concentration of concentrated seawater after seawater mixing Otherwise, it will not reach the salinity of seawater. For this reason, when diluting concentrated seawater to near the salinity concentration of normal seawater with seawater, diluted seawater more than the amount of intake seawater is required, and the pump equipment and enormous power required for this make the countermeasures substantially difficult. . On the other hand, if the seawater mixing ratio is lowered, the facilities and power for obtaining diluted seawater are reduced, but the salinity of concentrated seawater discharged into the sea area is increased. As a result, it becomes difficult to avoid the influence on the marine ecosystem due to the discharged concentrated seawater.

JP-A-8-132017

  As described above, in seawater desalination equipment, concentrated seawater is inevitably generated separately from the permeated water obtained as freshwater, so the release of this concentrated seawater to the sea area has an impact on the marine ecosystem. There is always concern.

  An object of the present invention is to provide a concentrated seawater desalination method for a seawater desalination device that can suppress the increase in salinity concentration in the discharge sea area and reduce the impact on the marine ecosystem when discharging the concentrated seawater from the sea water desalination apparatus to the sea area. It is to provide.

  The concentrated seawater discharge method of the seawater desalination apparatus of the present invention is the seawater freshwater which pressurizes the taken seawater and permeates the reverse osmosis membrane to obtain the permeated water, and releases the concentrated seawater that does not permeate the reverse osmosis membrane out of the system. It is characterized by mixing the concentrated seawater from the purification apparatus with the treated water discharged from the sewage treatment plant, and discharging the mixed concentrated seawater mixed with the treated water to the sea area.

  Also, the target concentration of salinity and concentration of concentrated seawater measured by the salinity concentration meter and the concentration seawater flow meter installed in the concentration seawater discharge pipe, which is the discharge pipe of the mixed concentration seawater, and the salinity concentration of the mixed concentration seawater A required treated water flow rate that is a flow rate of treated water from the sewage treatment plant is obtained based on the value, and a mixing ratio between the required treated water flow rate and the concentrated seawater flow rate is adjusted.

  In addition, if there is an excess of the treated water flow rate from the sewage treatment plant, excluding the required treated water flow rate to be mixed with the concentrated seawater, discharge the excess treated water flow rate from the treated water discharge branch pipe. It is characterized by.

  Also, the salinity of the mixed concentrated seawater is measured with a salinity meter, and the mixing ratio between the concentrated seawater and the sewage treated water is adjusted according to the deviation between the salt concentration setting target value of the mixed concentrated seawater and the measured salinity concentration. It is characterized by that.

  Also, a salinity meter that measures the salinity of seawater is placed in the discharge area of the mixed concentrated seawater, and according to the deviation between the salt concentration measured by the salinity meter and the preset salt concentration standard value in the discharge sea area. The mixing ratio between the concentrated seawater flow rate and the treated water flow rate is adjusted.

  Also, measure the salinity at multiple locations in the discharge area of the mixed concentrated seawater, select the maximum salinity among the measured salinity, and deviate between the selected salinity and the target salinity It is characterized by calculating | requiring.

  In addition, from the seawater desalination device that releases the concentrated seawater that does not permeate the reverse osmosis membrane from the seawater desalination device that pressurizes the taken seawater and permeates the reverse osmosis membrane to obtain the permeated water. When a salinity meter that measures the salinity concentration is installed and the measured value of the salinity meter is higher than the preset salinity concentration target value, the treated water from the sewage treatment plant is converted into the concentrated seawater before being discharged into the sea area. The mixed concentrated seawater after mixing and mixing is discharged into the sea area.

  In addition, the total flow rate of the treated water discharged from the sewage treatment plant to the outside of the system is mixed with the concentrated seawater discharged from the seawater desalination apparatus.

  In addition, the seawater taken is pressurized and permeated through a reverse osmosis membrane to obtain permeated water, and a seawater desalination device that discharges concentrated seawater that does not permeate the reverse osmosis membrane to the outside of the system, and treated inflow sewage to treat water And a sewage treatment plant that discharges out of the system, the concentrated seawater discharge pipe from which the concentrated seawater is discharged and the treated water discharge pipe from which the treated water is discharged are merged, and downstream of the concentrated seawater and the treated water after merging It is characterized by facing the side of the sea where concentrated seawater is discharged.

  Moreover, the installation position of the seawater desalination apparatus is lower than the installation position of the sewage treatment plant, and has a height difference.

  According to the present invention, the concentrated seawater discharged from the seawater desalination apparatus is mixed with the high salinity concentrated seawater discharged from the sewage treatment plant and discharged, whereby the concentrated seawater from the seawater desalination apparatus is discharged into the sea area. When discharging, a concentrated seawater discharge method of a seawater desalination apparatus is obtained in which the increase in salinity in the discharge sea area is suppressed and the influence on the marine ecosystem can be reduced.

It is a system block diagram explaining the concentrated seawater discharge method of the seawater desalination apparatus which concerns on Example 1 of this invention. It is a system block diagram of the seawater desalination apparatus of a present Example. It is a block diagram which shows an example of the processing system by the activated sludge method of the sewage treatment plant of a present Example. It is a related figure of the mixture ratio of a present Example, and the salt concentration after mixing. It is a system block diagram explaining the concentrated seawater discharge method of the seawater desalination apparatus which concerns on Example 2 of this invention. It is detail drawing of the system flow of the concentrated seawater discharge method of the seawater desalination apparatus of a present Example. It is a relationship figure of the mixture ratio and salt concentration target value of a present Example. It is a system block diagram explaining the concentrated seawater discharge method of the seawater desalination apparatus which concerns on Example 3 of this invention. It is a system block diagram explaining the concentrated seawater discharge method of the seawater desalination apparatus which concerns on Example 4 of this invention. It is a system block diagram explaining the concentrated seawater discharge method of the seawater desalination apparatus which concerns on Example 5 of this invention. It is a system block diagram explaining the concentrated seawater discharge method of the seawater desalination apparatus which concerns on Example 6 of this invention. It is a partial system block diagram explaining the concentrated seawater discharge method of the seawater desalination apparatus concerning Example 7 of this invention. It is a related figure of the salt ratio after mixing ratio and seawater mixing.

  In order to achieve the above-mentioned object, the inventors examined a method for suppressing an increase in salinity concentration in a discharge sea area when discharging the concentrated sea water from the sea water desalination apparatus to the sea area. As a result, when the concentrated seawater is discharged into the sea area, the treated sewage is treated at the sewage treatment plant and the treated water with low salt content discharged to the outside of the system is mixed with the concentrated seawater (hereinafter referred to as mixed concentrated seawater). It was clarified that if it is discharged into the sea area, the mixed concentrated seawater with reduced salinity concentration is discharged into the sea area, so that it is possible to suppress the increase in salinity concentration in the discharged sea area.

  In this way, in the seawater desalination device where concentrated seawater is discharged out of the system from the permeate water side of the reverse osmosis membrane, the intake seawater is pressurized and supplied to the reverse osmosis membrane as supply water, and concentrated. Seawater is mixed with treated water discharged from a sewage treatment plant, and mixed concentrated seawater mixed with treated water is discharged into the sea area.

  By mixing the concentrated seawater with the treated water discharged from the sewage treatment plant, the salt concentration in the mixed concentrated seawater mixed with the treated water is reduced, and the mixed concentrated seawater with a low salinity concentration can be discharged into the sea area. Therefore, compared with the case where the concentrated seawater discharged from the seawater desalination apparatus is directly discharged into the sea area, an increase in the salt concentration in the discharge sea area is suppressed.

  As a result, when the concentrated seawater is discharged from the seawater desalination device to the sea area, an increase in the salinity concentration in the discharge water area is suppressed, so a concentrated seawater discharge method for the seawater desalination device that can reduce the impact on the marine ecosystem is provided. can do.

  In addition, the required treatment water flow rate is obtained based on the target values set for the salinity concentration of concentrated seawater, the flow rate of concentrated seawater, and the salt concentration of mixed concentrated seawater, and the mixing ratio of the required treatment water flow rate and the concentrated seawater flow rate is adjusted. Features.

  When the concentrated seawater discharged from the seawater desalination unit and the treated water from the sewage treatment plant are mixed and discharged into the sea as mixed concentrated seawater, the sewage treated water flow rate mixed with the concentrated seawater flow rate is small, If the mixing ratio with the sewage treated water flow rate is not an appropriate value, the salinity of the mixed concentrated seawater becomes high without being sufficiently diluted. In this state, mixed concentrated seawater with a high salinity is discharged into the sea area, and there is concern about the impact on the marine ecosystem in the sea area.

  Therefore, based on the salinity concentration of the concentrated seawater obtained in advance, the salinity concentration of the concentrated seawater, the concentrated seawater flow rate, and the treated water are adjusted so that the salinity concentration of the mixed concentrated seawater after mixing the sewage treated water becomes the set target value. Based on the set target value of the mixed concentrated seawater after mixing, the required treated water flow rate to be mixed with the concentrated seawater is obtained, and the mixing ratio is adjusted. In this way, the salinity of the mixed concentrated seawater after mixing the sewage treated water is maintained at the set target value, and it is possible to eliminate the impact on the marine ecosystem associated with the release of the mixed concentrated seawater into the sea area. It becomes.

  In addition, as described above, when mixing the sewage treatment water with the concentrated seawater discharged from the seawater desalination apparatus, the mixing ratio between the concentrated seawater flow rate and the sewage treatment water flow rate is adjusted with the necessary treatment water flow rate. To do.

  In the seawater desalination apparatus, supply water (seawater) is pressurized to about 5 to 8 MPa by a high-pressure pump and supplied to the reverse osmosis membrane, and 30 to 60% of the supply seawater is recovered as permeate (freshwater). In this case, it is required to maintain a constant recovery rate in which the recovery rate (the amount of fresh water produced relative to the amount of supplied seawater) is set according to the selected reverse osmosis membrane. The operating condition of the seawater desalination apparatus is operated under the condition that priority is given to the recovery rate, and the pressure applied by the high-pressure pump is controlled to obtain a constant recovery rate.

  For this reason, if the recovery rate is constant, the permeate flow rate taken out as fresh water from the reverse osmosis membrane is also constant. On the other hand, the flow rate of the concentrated seawater discharged from the permeated water side of the reverse osmosis membrane is also constant, and the seawater desalination apparatus discharges the concentrated seawater at a substantially constant flow rate. For this reason, it is difficult to adjust the mixing ratio by increasing / decreasing the concentrated seawater flow rate. Rather, it is easy to adjust the mixing ratio by increasing / decreasing the necessary treated water flow rate by utilizing the characteristics of a constant flow rate.

  In this way, when adjusting the mixing ratio between the concentrated seawater discharged from the seawater desalination apparatus and the sewage treated water, and maintaining the salt concentration of the mixed concentrated seawater at the set value, the mixing ratio is adjusted. It can be easily adjusted by changing the flow rate.

  Also, measure the salinity of the mixed concentrated seawater after mixing the concentrated seawater and sewage treated water, and treat the concentrated seawater and sewage treatment according to the deviation between the salt concentration setting target value of the mixed concentrated seawater and the measured salinity concentration. The mixing ratio with water is adjusted.

  When mixing the sewage treatment water with the concentrated seawater from the seawater desalination unit and maintaining the salt concentration of the mixed concentrated seawater after mixing at the set target value, the salt concentration of the mixed concentrated seawater should be higher than the target value If there is, mixed concentrated seawater with high salinity will be discharged into the discharge sea area. As a result, there are concerns about the impact on the marine ecosystem in the released waters.

  Therefore, when discharging the mixed concentrated seawater to the discharge sea area, the salinity concentration of the mixed concentrated seawater is measured, and the mixing ratio is adjusted according to the deviation between the salinity concentration and the target value of the salinity concentration setting. . In this case, if the salinity of the mixed concentrated seawater is high, the amount of sewage treated water is increased by adjusting the mixing ratio according to the deviation from the target value, and the salinity of the mixed concentrated seawater is maintained at the target value. It will be. As a result, the mixed concentrated seawater is maintained at the set salinity concentration and discharged into the sea area, so that the influence on the marine ecosystem accompanying the release of the high salinity concentrated seawater is suppressed.

  In addition, a salinity meter that measures the salinity of seawater is placed in the discharge sea area of the mixed concentrated seawater, and the salinity concentration measured by the salinity meter is in accordance with the difference between the preset salt concentration standard value in the discharge sea area. Then, the mixing ratio of the concentrated seawater flow rate and the treated water flow rate is adjusted.

  When the concentrated seawater discharged from the seawater desalination unit and the sewage treated water are mixed and released into the sea as mixed concentrated seawater, if the dispersion of the mixed concentrated seawater does not proceed sufficiently in the released sea area, the salinity concentration increases. There is a fear. On the other hand, if the amount of sewage treated water with respect to the amount of concentrated seawater is small and there is a problem with the adjustment of the mixing ratio, the salinity concentration of the mixed concentrated seawater to be discharged increases. As a result, the marine ecosystem will be affected by this, and the discharge operation of mixed concentrated seawater based on the information on the salinity concentration in the discharge sea area will be required.

  Therefore, in order to adjust the mixing ratio between the concentrated seawater flow discharged from the seawater desalination unit and the treated water flow from the sewage treatment plant based on the salinity information in the discharge water area of the mixed concentrated seawater, it is placed in the discharge water area. The mixing ratio is adjusted according to the deviation between the salinity concentration measured by the salinity meter and the salinity concentration target value in the preset discharge sea area.

  In this case, if the measured salinity concentration in the discharge area of the mixed concentrated seawater is high, the mixing ratio is adjusted to a high level by increasing the sewage treatment flow rate according to the deviation from the target value of the salt concentration in the same sea area. The salinity concentration in the sea area will be maintained at the target value. As a result, the salinity concentration in the discharge sea area of the mixed concentrated seawater is maintained at the set salinity target value, and the increase in the salt concentration in the discharge sea area is suppressed, and the influence of the high salinity concentration on the marine ecosystem is suppressed. It can be solved.

  Also, according to the deviation between the measured value of salinity meter located in the discharge sea area and the target value of salinity concentration in the discharge sea area, the mixing ratio of concentrated seawater discharged from seawater desalination equipment and treated water from sewage treatment plant When adjusting, measure the salinity at multiple locations in the discharge sea area, select the maximum salinity among the measured salinity, and calculate the deviation between the salinity and the target salinity It is characterized by doing so.

  When the concentrated seawater released from the seawater desalination unit and the treated water from the sewage treatment plant are mixed and released into the sea as mixed concentrated seawater, the mixed concentrated seawater after release diffuses into the sea area. Are different under the influence of various conditions such as bottom topography, water depth, tidal flow velocity, discharge flow rate and discharge flow velocity in the discharge water area. In this case, if the mixed concentrated seawater is not diffused well into the sea area and the salinity concentration becomes high in a local area, this influence may cause an influence on the marine ecosystem.

  Therefore, in order to grasp the high salinity sea area locally in the discharge sea area, measure the salinity concentration at multiple locations in the discharge sea area and select the salinity value that shows the maximum value among the measured values. And the mixing ratio is adjusted according to the deviation between the salinity concentration target value in the discharge sea area.

  In this way, the sewage treatment flow rate is increased according to the deviation from the target value so as to reduce the salinity concentration in the discharge sea area according to the local high salinity sea area. The salinity concentration in the sea area will be maintained at the target value. As a result, it is possible to suppress the occurrence of local high salinity sea areas in the discharge sea areas, and to reduce the impact on the marine ecosystem.

  In addition, a salinity meter that measures the salinity concentration is arranged in the sea area where the concentrated seawater is discharged, and when the measured value of the salinity meter is higher than a preset salinity concentration target value, the treatment from the sewage treatment plant Water is mixed with concentrated seawater before being released into the sea area, and the mixed concentrated seawater after mixing is discharged into the sea area.

  Since the concentrated seawater is always discharged from the seawater desalination device to the sea area, the salinity concentration in the discharged sea area is higher than in other sea areas. For this reason, unless the salinity of the discharge sea area is reduced to the salinity of normal seawater, the impact on the marine ecosystem will increase.

  Therefore, in order to reduce the salinity of the concentrated seawater discharge area, a salinity meter is placed in the discharge area of the concentrated seawater to measure the salinity, and the measured value of this salinity is higher than the preset salinity target value. Is higher, the treated water from the sewage treatment plant for dilution is mixed with the concentrated seawater before being discharged into the sea area, and the mixed concentrated seawater with reduced salinity is discharged into the sea area.

  In this way, when the salinity concentration in the discharge sea area becomes higher than the target value, the discharged concentrated seawater is discharged into the sea area in a state lower than the initial salt concentration. As a result, the salinity of the discharge sea area where the salinity is higher than the target value is lowered, and the influence on the marine ecosystem in the sea area can be suppressed.

  In addition, as described above, when the salinity of the discharge sea area is higher than the salinity target value and the treated water of the sewage treatment plant is mixed with the concentrated seawater discharged from the seawater desalination device, The total flow rate of treated water is mixed with concentrated seawater discharged from a seawater desalination apparatus.

  If the salinity of the sea area becomes higher than the target value due to the release of the concentrated seawater from the seawater desalination system, it is necessary to quickly reduce the salinity of the sea area, and if the response time is delayed, the effect on the marine ecosystem May become enormous.

  Therefore, in order to quickly reduce the salinity of the sea area, the treatment water from the sewage treatment plant that dilutes the salinity of the concentrated seawater is mixed with the concentrated seawater to increase the mixing ratio of the treated water. It is. If it does in this way, since the salinity concentration of concentrated seawater will be diluted to the maximum and will be discharged to the sea area, the salinity density | concentration of the sea area where the salinity concentration became higher than the target value can be reduced rapidly. As a result, it is possible to quickly cope with ecosystems accompanying the increase in salinity in the discharge sea area.

  Further, the concentrated seawater discharge pipe from which the concentrated seawater from the seawater desalination apparatus is discharged and the treated water discharge pipe from which the treated water is discharged from the sewage treatment plant are joined, and the concentrated seawater is discharged downstream after the merge. It is in the sea area.

  With such a configuration, concentrated seawater with a high salinity concentration discharged from the seawater desalination device can be mixed with the treated water discharged from the sewage treatment plant, and the concentrated seawater diluted with the treated water can be used as seawater. It becomes possible to discharge to This makes it possible to suppress the influence on the marine ecosystem in the sea area rather than directly discharging the concentrated seawater having a high initial salinity.

  In addition, when the concentrated seawater discharge pipe from which the concentrated seawater from the seawater desalination unit is discharged and the treated water discharge pipe from which the treated water is discharged from the sewage treatment plant are merged, the installation position of the seawater desalination device is set at the sewage treatment plant. There is a difference in height between the installation position and the lower position.

  With such a position configuration, when the treated water discharged from the sewage treatment plant is mixed with the concentrated seawater discharged from the seawater desalination apparatus, it is possible to use the positional energy of the height difference, and when mixing the treated water For example, it is possible to mix treated water under natural flow without using equipment such as a water pump and power. As a result, when concentrated seawater is mixed with treated water from a sewage treatment plant and discharged into the sea area, costs such as power required for mixing can be reduced.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a system configuration diagram illustrating a concentrated seawater discharge method of a seawater desalination apparatus according to a first embodiment.

  The seawater W is taken from the sea area Sz by the intake pump 2 through the intake pipe 1 and sent to the seawater desalination apparatus 3 that uses a reverse osmosis membrane, and the seawater desalination apparatus 3 obtains the process described later from the seawater. Fresh water permeated water Fw is obtained and supplied to the demand end 6 by the water supply pump 4 through the distribution pipe 5 and the distribution pipe network 7. The water Rw used at the demand end 6 or the rainwater Rw flows into the sewage treatment plant 10 through the sewage pipe network 8 and the main trunk pipe 9 as sewage Ww. In the sewage treatment plant 10, inflow sewage is treated by obtaining a treatment process to be described later, and discharged out of the system as treated water Tw.

  The concentrated seawater discharge pipe 11 that discharges the concentrated seawater Cw from the seawater desalination apparatus 3 to the outside of the system and the treated water discharge pipe 12 that discharges the treated water Tw from the sewage treatment plant 10 merge. The downstream side of the merge pipe 13 after the merge faces the sea area Sz where the mixed concentrated seawater Cw is discharged.

  FIG. 2 is a system configuration diagram of the seawater desalination apparatus. As shown in FIG. 2, the seawater W to be subjected to the reverse osmosis membrane treatment is taken from the sea area Sz by the intake pump 1, stored in the raw water tank 21, and then sanded through the flowmeter 25 by the seawater pump 22. It is supplied to the filter 23 and the MF membrane device 24.

  The flow meter 25 measures the seawater supply flow rate Q to the sand filter 23 and the MF membrane device 24. The measured value Q of the flow meter 25 is input to the calculator 26. The computing unit 26 multiplies the measured value Q by the chlorine-based disinfectant injection rate CL separately input to obtain the chlorine-based disinfectant injection amount CQ, and the chlorine-based disinfectant injection pump 27 converts the chlorine-based disinfectant C into seawater. Injected into.

  Here, the chlorine-based disinfectant C may be injected on the suction side of the seawater pump 22 or may be injected before the flocculant injection described later. As the chlorine-based disinfectant C, chlorine water or sodium hypochlorite prepared by injecting chlorine gas into water is used, and microorganisms in seawater are disinfected or inactivated with the injection of the disinfectant.

  The measured value Q is input from the flow meter 25 to the calculator 28 and converted into the seawater supply flow rate to obtain the coagulant injection amount PQ. The calculator 28 is inputted with a preset flocculant injection rate P, and is multiplied by the seawater supply flow rate and the flocculant injection rate to obtain the flocculant injection amount PQ. The flocculant injection amount PQ is determined according to the flocculant injection amount PQ. Agent G is injected into seawater by a flocculant injection pump 29.

As the flocculant G, polyaluminum chloride or polysilica iron (SiO ₂ ) n · Fe ₂ O ₃ ) or the like is used, and the flocculant G injected into the seawater is stirred and mixed in a mixer (not shown). The turbid components in the seawater are converted into micro flocs, and the flocs are filtered by the sand filter 23. Components not filtered by the sand filter 23 are filtered by the MF membrane 24 on the downstream side, and then introduced into the treated water tank 30.

  In this embodiment, after the flocculant G is injected, turbid components are removed using the sand filter 23 and the MF membrane 24. However, an MF membrane, an NF membrane, or the like may be used. The turbidity removing means is not particularly limited.

  The treated water tank 30 is connected to a safety filter 32, and the treated water in the treated water tank 30 is pressurized by a high-pressure pump 31 connected to the safety filter 32, and is sent to the reverse osmosis membrane device 60 as supply water PW. The safety filter 32 is disposed on the suction side of the high-pressure pump 31 in order to prevent foreign matter from entering the reverse osmosis membrane 33 in the high-pressure pump 31 and the reverse osmosis membrane device 60.

  The supply water PW supplied to the reverse osmosis membrane device 31 by the high-pressure pump 31 is pressurized to about 5 to 8 MPa and supplied to the reverse osmosis membrane 33, and the permeated water FW is taken out as fresh water through the reverse osmosis membrane 33. Is done. The permeated water FW is stored in the permeated water tank 34, sterilized and added with minerals, and then supplied to the demand end 6 by the water pump 4.

  On the other hand, the concentrated seawater Cw that does not permeate the reverse osmosis membrane 33 is discharged from the permeate water side, and then energy is recovered by the pressure recovery turbine 35 and then discharged out of the system.

  FIG. 3 is a block diagram showing an example of a treatment system using an activated sludge method at a sewage treatment plant. As shown in FIG. 3, the sewage Is flowing into the sewage treatment plant 10 through the sewage pipe network 8 and the main trunk pipe 9 first flows into the aeration tank 37 through the settling basin 36, and in the blower 38 for a certain period of time. After being aerated with air, it flows into the final sedimentation basin 39. In the final sedimentation basin 39, the supernatant water and the precipitated activated sludge As are solid-liquid separated, and the supernatant water overflows and is discharged out of the system as treated water Tw. A part of the activated sludge As precipitated in the final sedimentation basin 39 is returned to the aeration tank 37 as return sludge Ra and used again for biological treatment.

  On the other hand, some activated sludge As is extracted out of the system as surplus sludge, and then dehydrated. In the inflow sewage treatment of the sewage treatment plant described above, the sewage treatment method by the activated sludge method of the process consisting of the first settling basin, the aeration tank and the final settling basin was adopted. The sludge method may be used, and the method for treating inflow sewage at the sewage treatment plant is not particularly limited.

  As described above, when the concentrated seawater discharge process of the seawater desalination apparatus 3 is configured, the concentrated seawater discharge pipe 11 from which the concentrated seawater Cw is discharged from the seawater desalination apparatus 3 receives the treated water Tw from the sewage treatment plant 10. Since it is merged with the discharged treated water discharge pipe 12, the treated water Tw discharged from the sewage treatment plant 10 and the concentrated seawater Cw are mixed and discharged to the sea area Sz as a mixed mixed concentrated seawater Ct.

  The concentrated seawater Cw discharged from the seawater desalination apparatus 3 has a salinity higher than that of seawater, but the treated water discharged from the sewage treatment plant 10 and the concentrated seawater Cw are mixed with the concentrated seawater Cw. By this, the salt concentration of the mixed concentrated seawater Ct after mixing decreases, and the mixed concentrated seawater Ct having a low salinity concentration can be discharged into the sea area.

  When the treated water Tw from the sewage treatment plant 10 is mixed with the treated seawater Cw and the seawater W is used, as shown in FIG. 4, the relationship between the mixing ratio M and the salinity concentration S is used. Compared to the same mixing ratio, the salinity S after mixing decreases. Here, when the mixing ratio M for reducing the salinity of the concentrated seawater Cw (assuming 6%) to the normal seawater salinity (3.5%) is obtained, the mixed water is mixed when the sewage treated water is mixed with the concentrated seawater Cw. The ratio W is as low as about 0.7, and the salinity concentration can be lowered with a small amount of treated water Tf with respect to the concentrated seawater amount Cf. On the other hand, when it is going to reduce the salt concentration of the concentrated seawater Cw using the seawater W, the mixing ratio M is as high as about 100 as shown in FIG.

In addition, the salt concentration S of the mixed concentrated seawater Ct after mixing the treated water Tw or the seawater W and the concentrated seawater Cw was obtained based on Equations 1 and 2.
(Equation 1)
S = {(Wo × Mb} + Ns / (1 + Mb)} (1)
(Equation 2)
S = {Ns / (1 + Mb)} (2)

  Here, S is the mixed concentrated seawater salinity concentration (%), Wo is the seawater salt concentration (3.5%), Mb is the seawater mixing ratio, and Ns is the concentrated seawater salinity concentration (6%).

On the other hand, although the mixing ratio M is expressed by Equation 3, the concentrated seawater amount Cf may be divided by the mixing amount Tf and expressed as the mixing ratio M. Further, as shown in Equation 4, the mixing ratio Mr may be used, and the mixing ratio or the mixing ratio is expressed by the same concept and is not particularly limited.
(Equation 3)
Mixing ratio M = (mixing amount Mf / concentrated seawater amount Cf) (3)
(Equation 4)
Mixing ratio Mr = (mixing amount Mf / (mixing amount Mf + concentrated seawater amount Cf) (4)

  Here, the mixed amount Mf = (the treated water amount Tf or the seawater amount Wf).

  Thus, compared with the case where the concentrated seawater discharged from the seawater desalination apparatus 3 is discharged directly into the sea area Sz, an increase in salinity concentration in the discharged sea area is suppressed.

  As explained above, since the concentrated seawater Cw from the seawater desalination apparatus 3 is mixed with the treated water Tw from the sewage treatment plant 10 and then discharged into the sea area Sz, an increase in salinity concentration in the discharged water area is suppressed. It can be set as the concentrated seawater discharge method of the seawater desalination apparatus which can reduce the influence on a marine ecosystem.

  A second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a system configuration diagram illustrating the concentrated seawater discharge method of the seawater desalination apparatus according to the second embodiment, and is configured in the same manner as in the first embodiment.

  The concentrated seawater discharge pipe 11 of the concentrated seawater Cw discharged from the seawater desalination apparatus 3 is provided with a concentrated seawater flow meter 40 for measuring the concentrated seawater flow rate Fc of the concentrated seawater Cw. A salinity meter 42 for measuring the salinity concentration Sc of the concentrated seawater Cw discharged from the seawater desalination apparatus 3 is installed. The salinity meter 42 samples the concentrated seawater Cw and measures the salinity concentration Sc.

  A treated water discharge pipe 12 for the treated water Tw discharged from the sewage treatment plant 10 is connected between the concentrated seawater flow meter 40 and the salinity concentration meter 42, and the treated water discharge tube 12 is discharged from the sewage treatment plant 10. A treated water flow meter 41 for measuring the treated water flow rate Ft of the treated water Tw is attached, and a treated water flow rate adjusting means 43 is disposed upstream of the treated water flow meter 41. That is, the treated water flow rate adjusting means 43 is disposed on the downstream side of the treated water discharge pipe 12 in the vicinity where it joins the concentrated seawater discharge pipe 11. The treated water flow meter 41 is connected to the treated water flow rate adjusting means 43 via the flow rate controller 46.

  A treated water discharge branch pipe 12A branched from the treated water discharge pipe 12 is installed, and an extra treatment excluding the necessary treated water flow rate Nw mixed with the concentrated seawater CW in the treated water flow rate Ft from the sewage treatment plant 10 is installed. When the amount of water is present, the treated water Tw is discharged from the treated water discharge branch pipe 12A to a discharge area (for example, a sea area).

  When comprised in this way, it operate | moves as shown in FIG. 6 which is a detailed figure of the system flow of the concentrated seawater discharge | release method of a seawater desalination apparatus.

The concentrated seawater flow rate Fc measured by the concentrated seawater flow meter 40 and the salinity concentration Sc of the concentrated seawater measured by the salinity concentration meter 42 are input to the treated water flow rate controller 44. The processing unit 45 of the treated water flow rate controller 44 requires the necessary treated water flow rate Nw to be mixed with the concentrated seawater based on the inputted concentrated seawater flow rate Fc, the concentrated seawater salt concentration Sc, and the set target value So of the salt concentration of the mixed concentrated seawater. Is calculated by Equation (5).
(Equation 5)
Nw = {Fc− (Sc / So) × Fc} (5)

  The necessary treated water flow rate Nw obtained by the computing unit 45 is input to the flow rate controller 46, and the treated water flow rate adjusting means 43 receives the flow rate signal of the treated water flow meter 41 in response to a signal from the flow rate controller 46. The opening degree is adjusted so that the treated water flow rate Nw is obtained.

The calculator 47 is supplied with the concentrated seawater flow rate Fc and the necessary treated water flow rate Nw obtained by the calculator 45, and calculates the mixing ratio M according to Equation 6.
(Equation 6)
M = Nw / Fc (6)

Note that when the fluctuations in the concentrated seawater flow rate Fc and the concentrated seawater salinity concentration Sc are small, as shown in FIG. The salt concentration setting target value So of the mixed concentrated seawater after mixing the water is input to obtain the mixing ratio M. Then, the obtained mixing ratio Mw and the concentrated seawater flow rate Fc may be input to the calculator 49, and the required processing flow rate Nw may be obtained according to Equation 7.
(Equation 7)
Nw = Fc × M (7)

  As described above, when the mixing ratio M of the concentrated seawater flow rate Fc and the treated water flow rate Nw mixed therewith is appropriately adjusted and the salt concentration of the mixed concentrated seawater is maintained at the set target value, the salt concentration of the mixed concentrated seawater is Can be arbitrarily reduced, so that the salt concentration does not increase. As a result, it is possible to eliminate the impact on the marine ecosystem associated with the release of high-concentration salinity mixed concentrated seawater.

  Also, when mixing the treated water TWw with the concentrated seawater Cw, without adjusting the concentrated seawater flow rate, adjust the required treated water flow rate to be mixed with the concentrated seawater Cw, and set the mixing ratio by increasing or decreasing this required treated water flow rate. By maintaining the value, the mixing ratio can be easily adjusted.

  A third embodiment of the present invention will be described with reference to FIG. FIG. 8 is a system configuration diagram for explaining the concentrated seawater discharge method of the seawater desalination apparatus according to the third embodiment, which is configured in the same manner as the second embodiment.

  In Example 3, a salinity meter 61 is installed in a pipe branched from the merge pipe 13, and the salinity meter 61 is the concentrated seawater Cw discharged from the seawater desalination apparatus 3 and the treated water Tw discharged from the sewage treatment plant 10. And the salinity concentration Cs of the mixed concentrated seawater Ct is mixed. That is, the salinity concentration meter 61 samples the mixed concentrated seawater Ct from the merging pipe 13 and measures the salinity concentration Cs.

  The arithmetic unit 52 of the corrected treated water controller 51 receives the set target value So of the salinity concentration Cs measured by the salinity concentration meter 42 and the salinity concentration of the mixed concentrated seawater Ct. The deviation ± ΔS of the salinity concentration Sc is obtained.

The calculator 53 for obtaining the necessary corrected treated water flow rate Nh receives the deviation ± ΔS obtained by the calculator 52, the concentrated seawater flow rate Fc discharged from the seawater desalination apparatus 3, and the set target value So of the mixed concentrated seawater. Then, the required corrected treated water flow rate Nh is obtained according to Equation 8.
(Equation 8)
Nh = {Fc− (± ΔS / So) × Fc} (8)

  The necessary corrected treated water flow rate Nh obtained by the computing unit 53 and the necessary treated water flow rate Nw obtained by the computing unit 45 or the computing unit 49 described in the second embodiment are input to the computing unit 54. Here, the required treated water flow rate Nw is increased or decreased to adjust the mixing ratio M.

  On the other hand, the necessary treated water flow rate Nw after the adjustment correction and the flow signal of the treated water flow meter 41 are input to the flow controller 46. By this flow rate controller 46, the treated water flow rate adjusting means 43 adjusts the opening according to the flow rate signal of the treated water flow meter 41 to adjust to the required treated water flow rate Nw after adjustment correction, and the salinity concentration Cs of the mixed concentrated seawater Ct. Is maintained at the set target value So.

  Thus, when the salinity concentration of the mixed concentrated seawater is measured and the mixing ratio is adjusted according to the deviation between the salinity concentration and the target value of the salinity concentration setting, even if the salinity concentration of the mixed concentrated seawater is high, According to the deviation from the target value, the flow rate of the treated water to be mixed is increased by adjusting the mixing ratio, and the salinity concentration of the mixed concentrated seawater is maintained at the target value. As a result, the mixed concentrated seawater is maintained at the set salinity concentration and discharged into the sea area, so that the influence on the marine ecosystem accompanying the release of the high salinity concentrated seawater is suppressed.

  A fourth embodiment of the present invention will be described with reference to FIG. FIG. 9 is a system configuration diagram for explaining the concentrated seawater discharge method of the seawater desalination apparatus according to the fourth embodiment, and is configured in the same manner as the third embodiment.

  The salinity meter 62 is disposed in the discharge sea area Sz of the mixed concentrated seawater Ct, and measures the salinity density Cz of the sea area Sz. The salinity concentration meter 62 includes a power storage unit (not shown) and an oscillation unit (not shown), has a mooring buoy, floats on the sea surface, and samples the seawater W with a built-in sampling pump (not shown). Then, the salinity Cz of seawater is measured.

  The measured value of the salinity concentration Sz is transmitted from the salinity concentration meter 62, and the measured value is received by the receiver 63 arranged on the ground. Note that the output from the salinity meter 62 may be transmitted to the ground via a cable.

  The measured value of the salinity concentration Cz measured by the salinity concentration meter 62 arranged in the sea area Sz is input to the corrected treated water controller 51 to obtain the necessary corrected treated water flow rate Nh, and the arithmetic unit described in the second embodiment The required treated water flow rate Nw and the required corrected treated water flow rate Nh obtained by 45 or the computing unit 49 are input to the computing unit 54, and the necessary treated water flow rate Nw is increased or decreased to adjust the mixing ratio M. On the other hand, the necessary treated water flow rate Nw after the adjustment correction and the flow signal of the treated water flow meter 41 are input to the flow controller 46. By this flow rate controller 46, the treated water flow rate adjusting means 43 adjusts the opening according to the flow rate signal of the treated water flow meter 41 to adjust to the required treated water flow rate Nw after adjustment correction, and the salinity concentration of the mixed concentrated seawater Ct Cs is maintained at the set target value So.

  Thus, the mixing ratio can be adjusted according to the deviation between the salinity concentration measured by the salinity meter arranged in the discharge sea area and the salt concentration target value in the preset discharge sea area.

  As explained above, when the measured salinity in the discharge area of mixed concentrated seawater is high, the mixing ratio is adjusted to be high by increasing the sewage treatment flow rate according to the deviation from the salinity standard value in the discharge sea area. The salinity in the sea area can be maintained at the target value. As a result, the salinity concentration in the discharge sea area of the mixed concentrated seawater is suppressed from becoming higher than the target value, and the influence on the marine ecosystem due to the high salinity concentration can be eliminated.

  A fifth embodiment of the present invention will be described with reference to FIG. FIG. 10 is a system configuration diagram for explaining a concentrated seawater discharge method of the seawater desalination apparatus according to the fifth embodiment, which is configured in the same manner as in the fourth embodiment.

  A plurality of salinity meters 62a, 62b and 62c are arranged in the discharge sea area Sz of the mixed concentrated seawater Ct, and measure the salinity concentrations Cz of the sea area Sz at a plurality of locations. Measurement values of the salinity concentration Sz are transmitted from the salinity concentration meters 62a, 62b and 62c, and the measurement value is received by the receiver 63 arranged on the ground.

  The determination device 71 selects a salinity concentration that indicates the maximum value among the salinity concentrations Cs1, Cs2, and Cs3 measured by the plurality of salinity concentration meters 62a, 62b, and 62c. The measured value of the selected salinity concentration Cs is input to the calculator 52 of the corrected treated water controller 51. Here, the necessary corrected treated water flow rate Nh is obtained, and the necessary corrected treated water flow rate Nh and the necessary treated water flow rate Nw obtained by the computing unit 45 or the computing unit 49 described in the second embodiment are input to the computing unit 54. The required treated water flow rate Nw is increased or decreased to adjust the mixing ratio M.

  The necessary treated water flow rate Nw after the adjustment correction and the flow signal of the treated water flow meter 41 are input to the flow controller 46. By this flow rate controller 46, the treated water flow rate adjusting means 43 adjusts the opening according to the flow rate signal of the treated water flow meter 41 to adjust to the required treated water flow rate Nw after adjustment correction, and the salinity concentration Cs of the mixed concentrated seawater Ct. Is maintained at the set target value So.

  Thus, in this example, in order to grasp the sea area of high salinity locally in the discharge sea area, the salinity concentration is measured at the number of places in the discharge sea area, and the salinity concentration showing the maximum value among the measured values. And the mixing ratio is adjusted according to the deviation between this measured value and the target salinity value in the discharge sea area. For this reason, in order to reduce the salinity concentration in the discharge sea area in accordance with the local high salinity sea area, the treated water flow rate is increased according to the deviation from the target value, and the mixing ratio is adjusted to be high. The salinity concentration at is maintained at the target value. As a result, it is possible to suppress the occurrence of local high salinity sea areas in the discharge sea areas, and to reduce the impact on the marine ecosystem.

  A sixth embodiment of the present invention will be described with reference to FIG. FIG. 11 is a system configuration diagram illustrating a concentrated seawater discharge method of the seawater desalination apparatus according to the sixth embodiment, which is configured in the same manner as in the first embodiment.

  A treated water discharge pipe 12 of the treated water Tw discharged from the sewage treatment plant 10 is connected to the concentrated seawater discharge pipe 11 of the concentrated seawater Cw discharged from the seawater desalination apparatus 3, and the treated water discharge pipe 12 is treated. Water flow rate adjusting means 43 is provided. The treated water discharge pipe 12b branched from the treated water discharge pipe 12 is also provided with a treated water flow rate adjusting means 43.

  The salinity meter 62 is disposed in the discharge sea area Sz of the mixed concentrated seawater Ct, and measures the salinity density Cz of the sea area Sz. The measured value of the salinity concentration Sz is transmitted from the salinity concentration meter 62, and the measured value is received by the receiver 63 arranged on the ground.

  The measured value of the salinity concentration Cs measured by the salinity concentration meter 42 is input to the calculator 52 via the receiver 63. The calculator 52 receives a salinity concentration setting target value So in the discharge sea area, and obtains a deviation ± Δ between the target value So and the measured salinity measured value Cs. When the deviation + Δ exceeds the target value So, the flow rate controller 46 opens the treated water flow rate adjusting means 43a and closes the treated water flow rate adjusting means 43b based on the output from the computing unit 52. Further, when the salinity concentration Cs of the discharge sea area is higher than the set target value So, the entire treated water flow rate is mixed with the concentrated seawater Cw as necessary.

  When the treated water flow rate control valve 43a is thus opened, the treated seawater Tw from the sewage treatment plant 10 is mixed with the concentrated seawater Cw from the seawater desalination apparatus 3, and the mixed mixed seawater Ct is used as the sea area. It will be discharged to Sz.

  In this embodiment, in order to reduce the salinity of the concentrated seawater discharge area, a salinity meter is arranged in the discharge area of the concentrated seawater to measure the salinity, and the measured value of the salinity is set in advance. When it is higher than the target value, the treated water is mixed with the concentrated seawater before being discharged into the sea area, and the mixed concentrated seawater with a reduced salinity concentration is discharged into the sea area. In this way, when the salinity concentration in the discharge sea area becomes higher than the reference value, the concentrated seawater to be discharged is discharged into the sea area in a state lower than the initial salt concentration. As a result, the salinity of the discharge sea area where the salinity is higher than the standard value is lowered, and the influence on the marine ecosystem in the sea area can be suppressed.

  Further, in this embodiment, when the salinity of the discharge sea area is higher than the target value of salinity and the treated water is mixed with the concentrated seawater, the total flow rate of the treated water from the sewage treatment plant is mixed with the concentrated seawater. I have to. If it does in this way, since the salinity concentration of concentrated seawater will be diluted to the maximum and will be discharged to the sea area, the salinity density | concentration of the sea area where the salinity concentration became higher than the target value can be reduced rapidly. As a result, it is possible to quickly cope with ecosystems accompanying the increase in salinity in the discharge sea area.

  A seventh embodiment of the present invention will be described with reference to FIG. FIG. 12 is a system configuration diagram illustrating the concentrated seawater discharge method of the seawater desalination apparatus according to the seventh embodiment, and is configured in the same manner as in the first embodiment.

  The concentrated seawater discharge pipe 11 from which the concentrated seawater Cw from the seawater desalination apparatus 3 is discharged and the treated water discharge pipe 12 from which the treated water is discharged from the sewage treatment plant 10 are connected so as to merge. And the downstream side after joining is made to face in the sea area Sz where the concentrated seawater Cw is discharged.

  In the present embodiment, the installation position of the seawater desalination apparatus 3 is arranged at a position lower than the installation position of the sewage treatment plant 10, and the both are set to have a height difference h.

  If it does in this way, the concentrated seawater with high salinity concentration discharged from the seawater desalination apparatus 3 can be mixed with the treated water discharged from the sewage treatment plant 10, and the concentrated seawater diluted with the treated water is used as the sea area. It becomes possible to discharge to This makes it possible to suppress the influence on the marine ecosystem in the sea area rather than directly discharging the concentrated seawater having a high initial salinity.

  Moreover, since the installation position of the seawater desalination apparatus 3 is set lower than the installation position of the sewage treatment plant 10, the treated water discharged from the sewage treatment plant into the concentrated seawater discharged from the seawater desalination plant. When mixing, it becomes possible to mix treated water under natural flow. As a result, when concentrated seawater is mixed with treated water from a sewage treatment plant and discharged into the sea area, costs such as power required for mixing can be reduced.

3 Seawater desalination equipment 4 Water pump 7 Water distribution network 10 Sewage treatment plant
11 Concentrated seawater discharge pipe 12 Treated water discharge pipe 33 Reverse osmosis membranes 42, 62 Salinity meter

Claims (10)

  Pressurized seawater to permeate a reverse osmosis membrane to obtain permeated water, and discharge the concentrated seawater that does not permeate the reverse osmosis membrane out of the system. A concentrated seawater discharge method for a seawater desalination apparatus, wherein the mixed concentrated seawater mixed with discharged treated water is discharged into a sea area.   The concentrated seawater discharge method of the seawater desalination apparatus according to claim 1, wherein the concentrated seawater measured by the salinity concentration meter and the concentrated seawater flow meter installed in the concentrated seawater discharge pipe which is the discharge pipe of the mixed concentrated seawater. Based on the salinity concentration and concentrated seawater flow rate, and the set target value of the salinity concentration of the mixed concentrated seawater, a required treated water flow rate that is the flow rate of treated water from the sewage treatment plant is obtained, and the required treated water flow rate and the concentrated seawater flow A concentrated seawater discharge method for a seawater desalination apparatus, characterized by adjusting a mixing ratio with a flow rate.   In the concentrated seawater discharge method of the seawater desalination apparatus according to claim 2, when there is an extra treated water flow rate excluding a necessary treated water flow rate mixed with the concentrated seawater from a treated water flow rate from a sewage treatment plant. A method for discharging concentrated seawater in a seawater desalination apparatus, wherein the excess treated water flow rate is discharged from a treated water discharge branch pipe.   The concentrated seawater discharge method of the seawater desalination apparatus according to claim 1, wherein the salinity concentration of the mixed concentrated seawater is measured by a salinity meter, and the salinity concentration setting target value and the salinity concentration measured value of the mixed concentrated seawater are calculated. A concentrated seawater discharge method for a seawater desalination apparatus, wherein a mixing ratio of concentrated seawater and sewage treated water is adjusted according to a deviation.   In the concentrated seawater discharge method of the seawater desalination apparatus according to claim 1, a salinity meter that measures the salinity concentration of seawater is disposed in the discharge sea area of the mixed concentrated seawater, and the salinity concentration measured by the salinity meter A concentrated seawater discharge method for a seawater desalination apparatus, characterized by adjusting a mixing ratio between a concentrated seawater flow rate and a treated water flow rate according to a deviation from a preset salt concentration standard value in the discharge water area.   The concentrated seawater discharge method of the seawater desalination apparatus according to claim 5, wherein the salinity concentration is measured at a plurality of locations in the discharge sea area of the mixed concentrated seawater, and the maximum salinity concentration is selected from the measured salinity concentrations. Then, a method for obtaining a deviation between the selected salinity concentration and the salinity concentration target value is provided.   From the seawater desalination device that releases the concentrated seawater that does not permeate the reverse osmosis membrane from the seawater desalination device that pressurizes the taken seawater and permeates the reverse osmosis membrane to obtain the permeated water, to the sea area where the concentrated seawater is discharged When a salinity meter for measuring the salinity concentration is arranged and the measured value of the salinity meter is higher than a preset salinity concentration target value, the treated seawater from the sewage treatment plant before being discharged into the sea area A method for discharging concentrated seawater of a seawater desalination apparatus, wherein the mixed concentrated seawater after mixing is discharged into the sea area.   The concentrated seawater discharge method of the seawater desalination apparatus according to claim 7, wherein the total flow rate of the treated water discharged from the sewage treatment plant to the outside of the system is mixed with the concentrated seawater discharged from the seawater desalination apparatus. Concentrated seawater discharge method of seawater desalination equipment.   Pressurized seawater is passed through a reverse osmosis membrane to obtain permeated water, and a seawater desalination device that discharges concentrated seawater that does not permeate the reverse osmosis membrane out of the system, and inflow sewage to treat treated water A sewage treatment plant that discharges to the outside of the system, and combines a concentrated seawater discharge pipe from which the concentrated seawater is discharged and a treated water discharge pipe from which the treated water is discharged; A method for discharging concentrated seawater in a seawater desalination apparatus, wherein the downstream side of the seawater is exposed to a sea area where the concentrated seawater is discharged.   The seawater desalination apparatus for discharging concentrated seawater according to claim 9, wherein the seawater desalination apparatus is installed at a position lower than the installation position of the sewage treatment plant and has a difference in elevation. Concentrated seawater discharge method for desalination equipment.

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